This invention relates to optical waveguides and particularly to a planar semiconductor waveguide capable of being switched.
The waveguide of this invention has been fabricated in GaAs with a p.sup.+ n.sup.- n.sup.+ structure and offers several advantages over striplines with n.sup.+ ribs; the junction device waveguide of this invention has a comparable or lower optical loss, and additionally allows high electric fields at low leakage currents to be applied to the guide by reverse-biasing the p.sup.+ n.sup.- junction. This property facilitates the fabrication of modulators and switches using electro-optic effects. Prior-art Schottky-barrier devices, which do permit electro-optical effects, and prior-art proton-bombarded embedded strips have higher losses than the p.sup.+ n.sup.- n.sup.+ guides of this invention and low loss guides are required for integrated optical circuit (IOC) applications.
Switching in this invention was achieved using a technique in which the phase synchronism of the coupled guides is destroyed via the electro-optic effect. Prior-art devices is GaAs based on this scheme used planar films. A GaAs switch using metal-gap strip guides also has been reported; however, this device had only about 75% power transfer and there was significant power loss at switching biases.
The prior-art waveguide structures present difficulties in fabrication, quality of performance, or versatility. Structures having a rib profile are difficult to fabricate as low-loss devices due to scattering losses associated with rib edge roughness. Moreover, due to the tapered sides of the ribs that occur in practice, it is difficult to place the guides sufficiently near for coupling while maintaining the electrical isolation needed to make a good electro-optic switch. The channel guide, at least in semiconductor materials (which at present must be used for monolithic IOC structures due to the inability to form lasers in the dielectric and glass materials useful for discrete waveguide devices) are not suitable for electro-optic switches because of the inability of simultaneously achieve low-loss propagation and high electric fields. The metal-gap waveguide has potentially high propagation loss (due to a portion of mode being under the metal layer) which could affect both guide and switch performance.
It is therefore an object of this invention to provide an improved optical waveguide which is relatively easy to fabricate and has good transmission properties.
It is a further object of this invention to provide an optical waveguide which can be switched or modulated by an electrical signal.
It is a further object of this invention to provide electro-optic modulators, directional couplers (power splitters) and electro-optic waveguide switches by fabricating two or more waveguides of this invention in proximity on a semiconductor substrate.